1. Field of the Invention
The present invention relates to a linear compressor available for a pulse tube type of cooling machine, and more particularly to a linear compressor equipped with a linear motor to drive a single piston unit forming part of the linear compressor to have the single piston unit perform a reciprocally linear motion. The present invention is concerned with an improved linear compressor so constructed as to ensure that the linear compressor effectively prevents vibrations thereof from being caused by a reciprocally linear motion of the single piston unit.
2. Description of the Related Art
Up until now, there have been proposed a wide variety of conventional linear compressors each equipped with a pair of linear motors to drive a pair of piston units forming part of the linear compressor to have each of the piston units perform a reciprocally linear motion.
The conventional linear compressors of this type have so far been available for such a pulse tube type of cooling machine for cooling a superconducting material used for an electronic component. The conventional linear compressor is operatively connected to the pulse tube type of cooling machine to have the pulse tube type of cooling machine supplied with a working fluid periodically compressed and decompressed by the conventional linear compressor.
One typical example of the conventional linear compressors is exemplified and shown in FIG. 8. The conventional linear compressor 200 thus proposed comprises a casing member 201 formed with a casing chamber 202, and a fixed member 203 accommodated in the casing chamber 202 of the casing member 201 and fixedly supported by the casing member 201. The fixed member 203 is formed with a hermetically sealed compression chamber 204 to receive a working fluid therein and an inlet-outlet port 205 having the working fluid introduced therein and discharged therefrom.
The conventional linear compressor 200 further comprises a connecting pipe 206 formed with a passageway therein and connected at one end to the fixed member 203 with the passageway held in communication with the inlet-outlet port 205 of the fixed member 203. The connecting pipe 206 is connected at the other end to the pulse tube type of cooling machine to have the working fluid fed to the pulse tube type of cooling machine through the passageway.
The conventional linear compressor 200 further comprises a pair of piston units 207 and 208 each including a piston head 207a and 208a axially movably received in the compression chamber 204 of the fixed member 203 and a piston rod 207b and 208b axially movably supported by the fixed member 203. The piston rods 207b and 208b are respectively connected to the piston heads 207a and 208a to have each of the piston heads 207a and 208a axially move in the compression chamber 204 of the fixed member 203. Each of the piston units 207 and 208 is axially movable with respect to the fixed member 203 under a reciprocally linear motion. The piston units 207 and 208 are located in symmetrical relationship with each other with respect to the compression chamber 204. The conventional linear compressor thus constructed is generally called xe2x80x9copposed piston type of linear compressorxe2x80x9d.
The conventional linear compressor 200 further comprises a plurality of resilient members 209 to 212 each intervening between the fixed member 203 and each of the piston units 207 and 208 to have the fixed member 203 and each of the piston units 207 and 208 resiliently connected with each other, and a pair of linear motors 213 and 214 designed to drive the piston units 207 and 208, respectively. Each of the linear motors 213 and 214 has an electromagnet unit 213a and 214a respectively mounted on the piston rods 207b and 208b, and a permanent magnet unit 213b and 214b supported by the fixed member 203 to have each of the piston units 207 and 208 perform the reciprocally linear motion. The linear motor thus constructed is generally called xe2x80x9cmoving coil type of linear motorxe2x80x9d.
The conventional linear compressor thus constructed, i.e., the opposed piston type of linear compressor, however, encounters the problem that the conventional linear compressor cannot be reduced in size, resulting from the fact that the large space of the conventional linear compressor is occupied by the pair of piston units located in symmetrical relationship with each other. This type of linear compressor further encounters the a problem that the conventional linear compressor is complicated in construction and thus expensive in production cost, resulting from the fact that the conventional linear compressor comprises the pair of piston units.
While it has been described in the above that the conventional linear compressor comprises a pair of piston units, the pair of piston units may be replaced by a single piston unit in order to have the conventional linear compressor reduced in size. The conventional linear compressor thus constructed is generally called xe2x80x9csingle piston type of linear compressorxe2x80x9d. This type of linear compressor, however, encounters the problem that the reciprocally linear motion of the single piston unit causes detrimental vibrations bringing mechanical failure brought to the conventional linear compressor.
Though the conventional linear compressor has been described in the above as being equipped with at least one of the moving coil type of linear motors, each of the moving coil type of linear motors may be replaced by a linear motor having a permanent magnet unit mounted on the piston rod and an electromagnet unit supported by the fixed member. The linear motor thus constructed is generally called xe2x80x9cmoving magnet type of linear motorxe2x80x9d. This type of linear motor is disclosed in the Japanese Patent Laid-Open Publication No. 6-189518. The conventional linear compressor equipped with at least one of the moving magnet type of linear motors, however, encounters the same problems as the conventional linear compressor equipped with the moving coil type of linear motor described in the above.
It is therefore a primary object of the present invention to provide a linear compressor that can effectively prevent the vibrations of the fixed member from being caused by the reciprocally linear motion of the single piston unit forming part of the linear compressor.
It is another object of the present invention to provide a linear compressor that can be reduced in size.
It is further object of the present invention to provide a linear compressor that can be simple in construction and thus inexpensive in production cost.
In accordance with one aspect of the present invention, there is provided a linear compressor, comprising: a fixed member formed with a hermetically sealed compression chamber to receive a working fluid therein; a movable member axially movably received in the compression chamber of the fixed member, the movable member axially movably supported by the fixed member to have the movable member axially move in the compression chamber of the fixed member; a plurality of resilient members each intervening between the fixed member and the movable member to have the fixed member and the movable member resiliently connected with each other, the movable member being axially movable with respect to the fixed member under a reciprocally linear motion to assume three different positions consisting of a compression position in which the working fluid is compressed by the movable member, a decompression position in which the working fluid is decompressed by the movable member, and a neutral position in which the movable member is resiliently retained by the resilient member s with respect to the fixed member under no influence of the working fluid in the compression chamber of the fixed member, driving means for driving the movable member at a predetermined driving frequency to have the movable member perform the reciprocally linear motion; damping means for damping vibrations of the fixed member caused by the reciprocally linear motion of the movable member, the damping means including a retaining member fixedly connected to the fixed member, a weight member axially movably supported by the retaining member to resonate with the vibrations of the casing member, and a resilient member intervening between the retaining member and the weight member to have the retaining member and the weight member resiliently connected with each other, first detecting means for detecting a displacement of the movable member with respect to the fixed member, the first detecting means being operative to produce a first displacement signal indicative of the displacement of the movable member; second detecting means for detecting a displacement of the weight member with respect to the retaining member, the second detecting means being operative to produce a second displacement signal indicative of the displacement of the weight member, and controlling means for controlling the predetermined driving frequency of the driving means to have the movable member perform the reciprocally linear motion at a predetermined phase difference between the first displacement signal produced by the first detecting means and the second displacement signal produced by the second detecting means to ensure that the vibrations of the fixed member are damped by the damping means when the movable member is driven by the driving means.
The linear compressor may further comprise an offset detecting means for detecting an offset of the movable member with respect to the neutral position of the movable member based on the first displacement signal produced by the first detecting means and second displacement signal produced by the second detecting means, the offset detecting means being operative to eliminate a signal component indicative of the offset of the movable member from the first displacement signal produced by the first detecting means when the offset of the movable member is detected by the offset detecting means.
The amplitudes of the movable member and the weight member may be coincident with each other.
The first detecting means may include an optical sensor having a photo emitter for emitting a light beam and a photo detector for detecting the light beam emitted from the photo emitter to the photo detector, the optical sensor being operative to produce the first displacement signal when the light beam emitted from the photo emitter to the photo detector passes over the movable member.
The second detecting means may include an optical sensor having a photo emitter for emitting a light beam and a photo detector for detecting the light beam emitted from the photo emitter to the photo detector, the optical sensor being operative to produce the second displacement signal when the light beam emitted from the photo emitter to the photo detector is interrupted by the weight member.
Each of the resilient members may include a plurality of leaf springs each having a plane extending perpendicular to the center axis of the movable member, each of the resilient members having a first portion fixedly connected to the movable member, and a second portion fixedly connected to the fixed member to ensure that the movable member is resiliently urged with respect to the fixed member toward the neutral position while the movable member is axially moved to the compression position and the decompression position thereof.
The driving means may include a linear motor having a first magnet unit in the form of an annular shape and mounted on the piston rod, and a second magnet unit in the form of an annular shape and supported by the fixed member, the first and second magnet units having respective center axes each held in coaxial relationship with the center axis of the movable member, and respective center planes each perpendicular to the center axis of the movable member, the center plane of the first magnet unit being on the center plane of the second magnet unit when the movable member assumes the neutral position.
The first and second magnet units may be constituted by an electromagnet and a permanent magnet, respectively, to ensure that the movable member is driven by the linear motor at the predetermined driving frequency of the electromagnet.
The damping means may be connected to the fixed member with the center axis of the weight member held in axial alignment with the center axis of the movable member.
The damping means may be connected to the fixed member with the center axis of the weight member held in parallel relationship with the center axis of the movable member.
The predetermined phase difference may be 180 degrees.